A critical requirement exists to acquire biological and clinical data from free-roaming ambulatory subjects for periods of time encompassing weeks to many months. The data acquisition system proposed will record such data at predetermined periods, or episodically when sensed data exceeds preset limits or special conditions detected. The system is capable of recording on magnetic tape (a microcassette) up to about 6-Mbytes - any datum which can be digitized - and is not limited to the recording of single parameters. Micropower circuitry, microprocessor control and ultra-low power incremental recording techniques are involved. Such a system, with its playback apparatus and associated software for a selected computer is appropriate for chronic studies of free-roaming cardiac patients, (the application of first choice) chronobiological studies, surveillance of drug-study subjects, determination of occurrence of petit-mal seizures, occurrence of anxiety episodes, etc. The design goal is a wearable, self-contained unit weighing approximately 150 g. with a volume of about 160 cc. It will contain sensor power control, sensor data preprocessing, digital conversion, buffer memory, mag-tape, tape drive, microprocessor control and batteries. We estimate there to be a substantial market for these systems in medical research and a large market in clinical applications.